Carrier telegraph system



Feb. 15 192 7 H. A. AFFEL CARRIER TELEGRAPH SYSTEM Filed Deo. 30. 1924 3Sheets-Sheet 1 ES SJ@ @a SN @u S, w

INVENTOR BM/ ATTORNEY H. A. AFFEL CARRIER TELEGRAPH SYSTEM Feb. 15 1927.

Filed Deo. 30. 1924 3 Sheets--Sheei'l 2 INVENTOR 5gg/7d BY C ATTORNEY H.A. AFFEL Feb. 15, 1927.

CARRIER TELEGRAPH SYSTEM Filed Deo. .30. 1924 3 Shets-Sheet 3 7ZRNEYNVENTOR ggf/yu E @a @l MN Patented Feb. l5, 1927.

UNITED STATES PATENT OFFICE.

HERMAN A. AFFEL, F MAPLEWOOD, NEW JERSEY, ASSIGNOR T0 AMERICAN TELE-PHONE AND TELEGRAPH COMPANY, A. CORPORATION 0F NEW YORK.

CARRIER TELEGRAPH SYSTEM.

Application led December 3 0, 1924. .Serial No. 758,881.

T his invention relates to carrier telelatter type of system usuallyenables the' employment of a greater number of carrier channels withinthe voice range than is possible in a band of equal Width above thevoice range where a system of the first type is employed. This followsfrom the fact that for a given spacing of the carrier frequenciesemployed, the frequency separation between any-two ladjacent frequencieswill be a greater percentage of the absolute carrier frequency in thecase of low frequency carriers, than in the case of high frequencycarriers; With a selective circuitor'given efficiency, it followstherefore that the low frequency carriers may be more closely spacedthan the high frequency carrlers.

Carrier telegraph systems of the second type above referred to have theobvious disadvantage that they may only be used upon telephone circuitswhere the circuits are not necessary for ordinary telephonetransmission. In accordance with the present invention it is proposed toutilize apparatus of the typeheretofore employed for carrier telegraphtransmission within the voice range-for 'obtaining an equal number ofcarrier telegraph channels in a band of the same width above the voicerange. This resu-lt may be obtained by first impressing signals on thelow frequency carriers and then modulating the low frequency telegraphcarriers with a carrier of high frequency, thereby producing side bandsyeach derstood from the following description containing individualbands corresponding to the low frequency carriers, and separated fromeach other by the same distance as the 10W` frequency carriers, 'thesebands, however, being elevated in the frequency spectrum with respect tothe original telegraph bands. One of the resultant side bands will besuppressed leaving only one stepped up band for each original telegraphband. Preferably, the carrier component resulting from the second stepof modulation will also be4 suppressed thereby reducing the energytransmitted over the circuits. At the receiving stations the stepped uptelegraph channels will be restored to their original frequency range bya corresponding demodulating step. The telegraph signais may thenbedetected from the low frequency carriers in the usual manner.

The invention may now be'more fully unwhen read in connection with theaccompanying drawing, Figures 1, 2 and 3 of which show circuitv diagramsillustrating three different embodiments of the invention.

Referring to `Fig. 1, a multi-frequency generator MG is illustrated forgenerating a plurality of carrier frequencies within the voice range.`This generator comprises a driving motor having an armature 50 and a'field winding 5l. vThe motor is arranged to drive a'- shaft carrying aplurality of toothed rotor members 53. Each rotor member will have adifferent number of teeth, the teeth being arranged to rotate in themagnetic field of polar magnetic structures such as 54. Suitable coils55 are wound about the pole pieces of the magnetic structures, and thesecoils are energized from a direct current source thereby producing afluxbetween the pole pieces which is varied'as the teeth of the rotormembers 53 rotate. Secondary windings 56 are also included in themagnetic structures. A1- ternating currents are induced in thesesecondary windings by the variations in flux produced in the magneticcircuits by the rotation of the rotor members.

'rliine conip one oit the inagnetic ciru 'L ee will depend upon the 1ecir shaft and the number on eacli rotor. in the case illust i erated arezn /Ts je. sei'erzl trcqu accordance iv to he frequencies fo, f1, yTiecurrents oit these may lie interrupted in repli code loy ineans and thecurrents may all cycli coininon transmission lie superposed circuit 53.

So tar the y tus described is similar to that enipioyed or multiplexcarrier telegraph transmission 'within tlie voice range, the trequenciesgenerated in the various magnetic circuits being relatively low requencies. orde to step up the carrier channeis to a poi shove tlie voicerange, a niodulatinfT .icinne is provided, this niais: rciatively highfrequency alterna or having a toothed rotor ineniber (Si) and a toothedstator member 59. The rotor nieiniaer is mounted upon a` shaft geared bysuitaiiie gearing (Si. to the shaft of the multi-frequency generatorpreviously described. Colis are wound upon each of the teeth ot thestator in order to provide the iieid windings ot tlie niacliine, thesecoils being connected to the transmission circuit 5S, carrying thesuperposed loW 'frequency carriers. Similar coils are also wound uponthe teeth ot the rotor, these Coils being connected through suitableslip rings to`a circuit t2 connected throughaiilter 63 to the tinsinission line L. 'lilie 1nachine TM, when its eld Winding is excitedby carrier frequencies produced loy the inuiti-trequency generator,operates as a modulating device, producing two side bands. rihe carriercomponent itself is suppressed, however, as the rotor windings are onlyenergized When tlie low 'frequency modulated carriers are impressed uponthe circuit 58 and the magnetic tina in the stator' Windings is at alitimes directly nroportional to the ampiitude et tlie energizingcurrents. The filter 63 is designed to suppress one of the side handsresulting from the modulating action ot' the machine "En At the distantstation siniiiar rnulti-ti-e qnencgr generator MCT. is provided, tliisgenerator and its associated circuits being identical in sii respects tothe multi-frequency generator MG- ali'eady described, except that thedriving niotor is provided with an auxiliary Winding 522 in .additiontothe field Winding 5i, the auriiiar'y Winding being rovided for apurpose-Which will more iully appear einatten it inoduiating machine Tlf siM ar to the machine TM alaiso provided at the disti-fre( nene fGererator MG'. scaring" 5 ratio is iliade diri-ere t in tliis case,ioivcvcr, in order that the eti'ec l l tive carrier irequency ot themodulating' inaclnne Wiil lie sucli as to step up tlie losv trequencybands to a range differenttroni the modulating niacliine TM. The rotorwindings ot the nioduiating machine Titi are connected iiy a circuit 62to tiie line L through a iiiter $3 which is designed to suppress one ofthe side hands generated lay tlic inodulator.

A. demodulating machine RM is aiso provided at the distant station, thismachine lacing similar in its construction to the niodulating machineaiready received. The stator windings of this machine, lioivever, areconnected to the iine L tlirougii a filter 64, this filter beingdesigned to pass the saine hand ot' frequencies as the iilter G3. llierotor windings ot' the machine BM are connected through suitaliie slipri g circuit 65. The action of tlie inaciiine RM is to beat tliereceived hand ot carrier i`requencies with a frequency corresponding tothe carrier frequency of tiie modulator Tlii thereby' producing"difference frequencies corresponding to the originai ioiv frequencycarriers impressed upon tlie circuit 58. rllliese stepped downfrequencies are therefore impressed upon the circuit G5. i plurality ofbranch-receiving circuits are connected with the circuit 65 through`filters such as 6G, these iilters being arranged to select the originalcarrier rcquenciessucli as f2, etc. Suitable detecting devices et a wellknown type are conventionally indicated at o?, these detecting devicesbeing included in tlie individuai tiranciies for the purpose ot'detecting troni the loir frequency received carriers direct currentimpulses corresponding to tlie telegraph signais transmitted luy thekeys 57 at the transmitter. Receiving relays or Sounders suoli as 68 areconnected to the detectors to be actuated hy t-lie detec-ted telegraphcurrents.

At the station Wliere the motti-frequency generator lil/il@ is located,r ceiving equipment similar to that just descr hed is aise provided,this receiving equipment comprising a dernoduiating machine RM geared tothe shaft et the niuit'iale generator MG, the ratio ot the gearing seingsuch that the lieating frequency et the deniodilating machine RM will hethe saine as carrier tre quency ot the inoduiating machine TM, assuming,ot course, that the drying shafts or" the multi-frequency generators Mtrand MG are rotated tiie saine speed. The rest ci? the receivingequipment is identicai with that already described need not he furtherdiscussed.

For tlie proper 't ratus above discicsec, it is desirable that themotors driving site raciti-frequency genertliose transmitted liv lil()ators MG 'and MG rotate at the same speed. In order to accomplish thisresult, one of the frequencies generated by the multi-frequencygenerator MG, for example, the frequency fm is utilized as asynchronizing frequency. This frequency is stepped up by thetransmitting modulator TM along With the other low frequency carriers,and upon being translnitted to the distant. station is demodulated bythe demodulating machine RM to restore it to its original frequencylevel. A filter 69 is connected in a branch leading from the circuit totransmit the received synchronizing frequency to a suitable detector 70.The corresponding frequency fo generated by the multi-frequencygenerator MG is led olf from the machine through a similar filter 71, sothat this frequency 1s also impressed upon the input circuit of thedetector 70. The output circuit of said detector includes the auxiliaryWinding 52 previously referred to. y

lVhenever the motor driving the shaft of the machine MG tends to changeits speed, the frequency f, generated by the machine will be differentfrom the frequency 72, generated by the machine MG and selected from thecircuit (S5 by the filter 69. The detected direct current component inthe output circuit of the detector will have a given amplitude when thelocal frequency fo and the received frequency f", are in synchro-l nism,but as these two frequencies depart from synclnronism the detecteddirect current component changes in amplitude. Consequently, when themotor driving the multi-frequency generator MG changes its speed withtheresult that the locally generated frequency fo departs from synchronismwith the received frequency fo, the energizing current in the auxiliaryWinding 52 of the motor will change in value. The magnetic fiuX of thefield of the motor will 'therefore be changed to restore the motor toits original speed. The motor driving the multi-frequency generator MGwill therefore rotate at the same speed as the motor driving themulti-frequency generator MG, and consequently the carrier frequenciesof the transmitting modulator TM and lreceiving demodulator RM will bethe same. Likewise the carrier frequency of the transmitting modulatorTM and the receiving modulator RM will be the same.

The various frequencies generated by the.

produce in the rotor windings two side bands, each includlng componentscorresponding to the origlnal low frequency carriers, these side bandsbeing related to a carrier suppressed by the machine, the frequency ofthis carrier being determined by the number of teeth in the machine andthe speed of rotation. This carrier is assumed to be a frequency fc. Oneof the side bands, for example, the lower side band, is suppressed bythe filter 63 which transmits the upper side band ffl-(fn tofs).

This side band, it will be noted, contains frequencies corresponding toeach of the original frequencies fo to f6, inclusive, and thesefrequencies are transmitted over the line L and passed through thefilter 64 to the stator windings of the 'demodulating machine RM. Themachine RM beats the received band with a frequency fc to produce sumand difference frequencies. The difference frequencies corresponding tothe original frequencies fo to fc, inclusive, are impressed upon thecircuit 65. The frequencies f1 to f, carrying the telegraph signals areselected by the filtersA 66, and the telegraph signals al'e in turndetected by the detectors 6,7 to operate the individual receivingdcvices. The frequency fo, which carries no signals, passes through thefilter 69 to eontrol the synchronizing arrangement, as alreadydescribed.

Transmission in the opposite direction by means of the frequenciesgenerated by the multi-frequency generator MG is similar to that alreadydescribed herein. It should be noted, however, that the frequency fogenerated by the machine MG is not used for synchronizing purposes whenreceived at the distantend, and consequently this frequency may beinterrupted by means of a suitable key to transmit telegraph signals. Itfollows therefore that the arrangement above described involves one lesstelegraph channel for transmission in one direction than in the case oftransmission in the other direction, the omitted channel being used forsynchronizing purposes.

A modified arrangement is illustrated in Fig. 2, this arrangement emloying vacuum 'tube modulators and demo ulators for the stepping up andstepping down operation. The' carrier frequencies for the modulators`and demodulators are supplied by a harthe multi-frequency generator MGBIn order to provide the carrier frequency for enfying the selectedharmonic and impressing it upon'the modulator. A second filter 7 9 isprovided fpr selecting another harmonic, for example, yf, to be used asthe carrier for supplying the receiving demodulator at the same station.This demodulator comprises a balanced vacuum tube arrangement 80 havingits input circuit connected through the filter 64 to the line L. Theharmonic which is selected bythe filter 79 is amplified by a suitableamplifier 81 and impressed upon the common branch of the input cir-`cuit of the demodulator. I

The modulator 7 3 and the -demodulator 80 at the distant station aresimilar to the corresponding devices already described. The basefrequency from which the carriers are to be generated is in thisinstance obtained from ,the circuit by means of a filter 82. This freuency is impressed upon a distorting devlce 75 thereby producingharmonics corresponding to ivf, and yfo, the former being impressed uponthe detector 80 and the latter upon the modulator 73.

The various low frequency carriers fo to f6, inclusive, are impressedthrough the circuit 58 upo the modulator 73. The frequency f, is alsoimpressed upon the distorting tube 75, las already described,therebyproducing the harm'oniefvf0 for supplying the carrier ;othemodulator 73. The modulator produces upper 'and lower side bandscontaining frequencies correspondin to the frequencies generated by themultirequency generator MG The carrier frequency wf, is suppressed,however, b the balanced arrangement of the modu ator 73. The filter 63suppresses one of the side bands, say the lower side band, and the upperside band is transmitted over the line L and through the filter 64 tothe demodulator 80. The harmonic wf, supplied to the demodulator 80 bythe distorting device 75 beats with the received band to producedifference frequencies correspondin to the original frequencies fo tof6, inclusive. The frequencies f, to f6, inclusive, carrying signals,are detected to operate the receiving devices in the manner alreaddescribed. The controlling frequency f, 1s selected by the filter 82 tocontrol the harmonics generated by the harmonic generator 75Transmission in the op osite direction will be similar to ythat alrea ydescribed except that in this case the frequency fo generated by themachine MG is used for signaling, this frequency not being necessary asa controlling frequency for transmission in this direction.

Fig. 3 shows an arrangement in which all of the frequencies generated bythe multifrequency generators MG and MG may be utilized for transmittingsignals. This is accomplished by arranging the motors driving themulti-frequency generators so that the speed of each motor is controlledlocally by a constant frequency device, such, for example, as a tuningfork of great frequency stability. It is' therefore unnecessary totransmit the frequency fo uninterrupted by signals to the distantstation to control the motor thereat.

The synchronizing apparatus -in detail comprises a tuning fork 83 havingone of its vibrating tines arranged to operate a current changingdevice, such, for example, as a microphone 84, included in the localcircuit with a magnet 85. The magnet 85, as

the current therethrough is varied at a frequency determined by thenatural period of the tuning fork, acts upon the tuning fork to keep itcontinually in vibration at its natural frequency. Part of the energy ofthe frequency fo generated by themulti-frequency generator MG is passedthrough a filter 86, and this frequency flows through a secondmicrophone device 87 which is also operated by the tuning fork. Theauxiliary winding 52 of the motor is connected in circuit with themicrophone 87 which acts as a modulator so that a direct currentcomponent is supplied to the auxiliary winding 52 rdepending on thesynchronization of the frequency f, transmitted through the filter 86with thc frequency of vibration of the microphone 87. Any tendency ofthe motor 50 to vary its speed is therefore counteracted by the,compensatingcurrent supplied to the Winding 52;

A similar apparatus is provided at the distant station for controllingthe motor thereat. In each case the frequency fo of the multi-fre uencygenerator is used locally for contro ling the speed of the motor.Consequently this frequency may in both cases be used for telegraphsignals by providing a suitable key to interrupt the transmission of thefrequency to the circuit 58 or 58', as the case may be. The modulatingand demodulating apparatus TM, RM, etc., for stepping up and steppingdown the frequencies is of the t pe illustrated in Fig. l, and theoperation uring transmission in either direction Will be clear Withoutfurther description.

It will be obvious that the general principles herein described may beembodied in many other organizations Widely different from thoseillustrated Awithout departing taining carrier frequencies correspondingto from the spirit of the invention as defined in the following claims.A

What is claimed`isz..

1. In a carrier telegraph s stem, means to generate a l plurality of elcarrier frequencies within the voice range,

means to impress. separate telegraph signals u onhthe various carrierfrequencies, a modu ator having an effective carrier frequency whoseratio is defined with respect to oneoof said first mentioned carrierfrequencles,

means to determine said ratio, means to im'-,I

press the various bands resulting from si naling upon said modulator toproduce si e bands at' least one of which is above the voice range,means tol transmit a side band above upon saidfmodulator to produce sidebands the voice' range,the transmitted band comrising sub-bandscorresponding'to the origmal bands and having the same frequencyseparation.

2. In a carrier telegraph system, means to generate a plurality ofclosely spaced carrier frequencies within the voice range,

means to impress separate telegraph signals upon the various carrierfrequencies, a modulator having an effective carrier frequency whoseratlo is defined with respect to one of said first mentioned carrierfrequen cies, means to determine said ratio, means to impress thevarious bands resulting from signaling upon said modulator to produce s1e bands at least one of which is above thevoice range, means to transmita side band above the voice ran e, the transmitted band comprisingsub-ban s corresponding to the origlnal' bands and having the samefrequency separation, a demodulating apparatus at the receiving stationfor effectively` beating the received transmitted band with an effectivecarrier frequency bearing a definite ratio to one of the originallygener- -ated carrier frequencies, means to determine said last mentionedratio, means to select from said demodulating apparatus bands within`the voice range corresponding to the original bands, and means] toseparately detect signals from lsaid bands.

3. In a carrier signaling system, a multifrequency alternator forgenerating aplaralit of closely spaced carrier fre uencies withln thevoice range, one of said requencies being a controlling frequency, meansto impress signals upon the carrier frequencies, a modulator havin aneffective carrier frequency bearing a efined ratio to said controllinfrequency, means controlled by said contro ling frequency to determinesaid ratio, means to apply .said controlling frequency to ether withother frequencies generated i y said multi-frequency alternator uponsaid modulator to produce lside bands at least one of which is above thevoice range, and means to transmit one of said side bands, saidtransmitted side band conosely spaced frequencies generated by saidmulti-frequency generator and having thesame frequency spacing.

4. In a carrier signaling system, a multifrequency alternator forgenerating a plurality of closely spaced carrier frequencies within thevoice range, one of said frequencies being a controlling frequency,means to impress signals upon the carrier frequencies, a "5 modulatorhaving an effective carrier frequency bearing a definite ratio to saidcontrolling frequency, means controlled by said cont-rolling frequencyto determine said ratio, means to apply said controlling frequencytogether with other frequencies generated by said multi-frequencyalternator one of which is above the voice range, means to transmit oneof said side bands, said transmitted side band containing carrierfrequencies corre n to the frequencies generated by said multl-frequencygenerator and having the same frequency spacing, a demodulatingapparatus at the receiving station for effectively beatin the receivedtransmitted band with an eective carrier frequency bearing a definiteratio to said controlling frequency, means to detect from saiddemodulating apparatus said controllingfrequency and bands Within thevoice range corresponding to the original bands, means to separatelydetect signa sfrom said bands, and meanscontrolled by said detectedcontrolling frequency'to determine said last mentioned ratio. 45. In acarrier signaling system, a multifrequency alternator for generating aplurality of closely spaced carrier fre uencies within the voice range,one of said requenles cies being a controlling frequency, means toimpress signals upon the carrier frequencies, a modulator having aneffective -carrier frequency bearing a fixed ratio to said controllingfrequency, means to apply said con- 1m trolling frequency together withother frequencies generated by said mult1frequency alternator upon saidmodulator to produce side bands at least one of which is above the voicerange, means to sup ress the ca r- 115 rier frequency component an oneof said lside bands while transmitting the other side 'effective carrierfrequency the same as the effective carrier frequency of the modulator,means to select from the demodulator frequencies Within the voice rangecorresponding to the frequencies generated by said multi-frequencygenerator, and means to detect signals from said frequencies.

6. In a carrier signaling system, a'motordriven multi-frequencyalternator for generating a plurality of closely spaced carrierfrequencies Within the voice range, `means to impress signals on saidcarrier frequencies, a modulating alternator for producing an effectivecarrier frequency to which the modulated bands corresponding to themodulated carriers of the multi-frequency generator may be a plied, saidmodulating alternator being riven by the motor which drivessaidmulti-frequency alternator so thatfthe effective carrier frequency ofthe modulating alternator will bear a fixed ratio to at least one of thefrequencies generated by the multi-frequency alternator, means to selectfrom the output'of said modulating alternator a band comprising aplurality of sub-bands corresponding to the originally modulated bandimpresed upon the modulating alternator.

7. In a carrier signaling system, amotordriven multi-frequencyalternator for generating a plurality of closely spaced carrierfrequencies Within the voice range, means to impress Vsignals on saidcarrier frequencies, a modulating alternator for producing an effectivecarrier frequency to which the modulated bands corresponding to themodulated carriers of the multi-frequency generator may be applied,"said modulating alternator being driven by the motor which drives saidmulti-frequency alternator so that the effective carrier frequency ofthe modulating alternator Will bear a fixed ratio to at least one of thefrequencies genof said modulating alternator, means to se' lect from theoutput of said demodulating alternator frequencies corresponding to tbefre uencies originally generated by said mu ti-freq'uency generator, andmeans to detect signals from said selected frequencies.

8. In a carrier telegraph system, a multifrequency alternator forgenerating a controlling frequency and a plurality of car' rierfrequencies within the voice range, a motor for driving said alternator,means for impressing signals upon said carrier frequencies, a modulatingalternator upon which the resultant signaling bands may be impressed,means whereby said motor for driving said multi-frequency generator willdrive said modulating alternator to produce an effective carrierfrequency bearing a constant ratio to said controlling frequency, andmeans to select from the output of said modulating alternator a band offrequencies comprising a plurality of sub-bands corresponding to theoriginal carrier bands.

9. In a carrier telegraph system, a multifrequency alternator forgenerating a controlling frequency and a plurality of carrierfrequencies Within the voice range, a motor for driving said alternator,means for impressing signals upon said carrier frequencies, a modulatingalternator upon which the resultant signaling bands may be impressed,means whereby said motor for driving said multi-frequency generator willdrive said modulating alternator to produce an effective carrierfrequencv bearing a constant ratio to said controlling frequency, meansto select from the output of said modulating alternator a band offrequencies comprising a plurality of sub-bands corresponding to theoriginal carrier bands, a demodulating alternator at the receivingstation, a motor for driving said demodulating alternator to produce aneffective beating frequency corresponding to the effective carrie-rfrequency of said modulating alternator, means to select from the outputof said demodulating alternator frequencies coiesponding to the originalfrequencies modulated by the multi-frequency generator, means to detectsignals from said fre- 100 quencies, and means to control the speed ofsaid last mentioned motor in accordance with a component selected fromthe output of said demodulating alternator and corresponding to saidcontrolling frequency,

l0. In a carrier telegraph system, a multifrequency generator forgenerating a plurality of closely spaced carrier frequencies Within thevoice range, a motor for driving said generator, means to impresssignals 11o upon said carrier frequencies, a modulating alternator,means to impress the signaling band resulting from said signals uponsaid modulating alternator, means whereby said alternator may be drivenby the motor for 115 driving said multi-frequency generator so as toproduce an effective carrier frequency so chosen as to produce sidebands at least one of which is above the voice range, means to selectand 'transmit one of said side bands 120 above the voice range,apparatus similar to that above described at a distant station `butdiffering therefrom in that the modumodulating alternators being drivenby the motors for driving the multi-frequency generators at each stationat'. speeds suchv that each demodulating alternator will produce aneiectivebeating frequency corresponding to the e'ective carrierfrequency of the modulating alternator at the other station,

means to select from each demodulating alternator frequenciescorresponding to the frequencies generated by the multi-frequen- 10 cygenerator at the other station, and means to detect signals fromtheselected frequencies.

In testimony whereof, I have signed m y name to this specification this29th day of 15 December, 1924.

HERMAN A. vAFFEL.

